1. Field of the Invention
This invention relates to cooled gas turbine blades and more particularly to a blade having a liquid coolant flowing through fluid distributing channels subjacent the surface of the blade.
2. Description of the Prior Art
Liquid, i.e., water, cooled gas turbine blades are shown in U.S. Pat. Nos. 3,804,551 and 3,736,071. In these patents water enters the blade adjacent the blade root and is exhausted at the blade tip as a mixture of steam and water. However, it is recognized that the presence of steam in heat transfer tubes, such as the channels distributing the coolant through the blade, substantially reduces the ability of the water within the channels to absorb the heat from the surrounding structure. This is because the steam produces pockets or voids in the water that prevents the water from wetting the walls of the passages and absorbing the heat therefrom.
U.S. Pat. No. 3,902,819 shows another cooled turbine blade, and in an attempt to overcome the above deficiency, maintains the water at a super critical pressure so that it cannot pass through the phase change to steam, thereby remaining liquid and in intimate heat transfer contact with the walls of the channels. However, this reduces substantially the amount of heat that can be absorbed by the liquid if permitted to change phase from water to steam, which heat must come from the surrounding blade structure thereby cooling it. Thus the advantages obtained within a cooling system by permitting a phase change and thereby increasing the cooling capability of the water have heretofore been negated by subsequent decrease in heat transfer rates due to the vapor generated by the phase change subsequently interfering with heat transfer into the remaining liquid flowing through the coolant channels, and elimination of the phase change of the coolant from liquid to vapor likewise reduces the coolant's capacity to absorb heat.